Large diameter earth drill

ABSTRACT

A system for producing large-diameter, air-drilled holes through rock comprises a hollow, rotatable drill stem having a large bit at its lower end, and surrounded by a pipe which is relatively narrow compared to the hole diameter, which forms between itself and the drill stem, an annular passage. Air is blown downwardly through the drill stem, emerges at an opening at the location of the bit, and carries cuttings through the annular passage to the surface. A vacuum is drawn in a dust diverter immediately above the bit to insure that the cuttings enter the annular passage. Air descending through the drill stem under pressure operates a piston which imparts a hammering action to the bit. Drill stem sections and outer pipe sections may be added as required.

United'States Patent a 11 1 3,655,001 1451 Apr. 11,1972

3,297,100 l/l967 Crews ..17s/21s x Prime/y Eraminer bavid H. Brown-Attorney-Bauer, Smith Harding [57] ABSTRACT A system for producinglarge-diameter, air-drilled holes through rock comprises a hollow,rotatable drill stem having a large bit at its lower end, and surroundedby a pipe which is relatively narrow compared to the hole diameter,which forms between itself and the drill stern, an annular passage. Airis blown downwardly through the drill stem, emerges at an opening at thelocation of the bit, and carries cuttings through the annular passage tothe surface. A vacuum is drawn in a dust diverter immediately above thebit to insure that thecuttings enter the annular passage. Air descendingthrough the drill stern under pressure operates a piston which imparts ahammering action to the'bit. Drill stem sections and outer pipe sectionsmay beadded as required.

16 Clalrns,5 Drawlng Figures BACKGROUND OF THE INVENTION This inventionrelates to apparatus for producing large diameter holes in earth androck for the purpose ofsetting poles, piling and the like. Typicaldiameters are in the range of 16 to 24 inches, although still largerdiameters are sometimes required in certain applications. I In the past,these holes have been produced by blasting and also by producing leadholes of small diameter, for example 6 inches, and subsequently reamingto the required dimensions. Attempts to produce large holes have alsobeen made involving the use of large diameter drills. The equipmentrequired was bulky, and in many instances several passes had to be madewith the drill because of difficulties in removing cuttings.

Air drilling has simplified the removing of cuttings in small diameterdrills. Typically, a rotating drill stem is provided with a centralpassage and a surrounding annular passage. Ordinarily, air is introducedunder pressure through the central drill stem passage, and cuttings areremoved along with air through the annular passage. In reversecirculation" air drilling, air is introducedunder pressure through theannular passage, and cuttings are removed along with the air through thecentral passage.

Heretofore, neither of these methods has been successfully employed inthe drilling of large diameter holes.

Numerous difficulties have been encountered in air drilling. Theproduction of 'dust clouds by the air stream at the bit has resulted inunpleasant, and possibly hazardous conditions for drill operators andother persons in the vicinity of a drilling operation.

SUMMARY OF THE INVENTION In accordance with this invention, a rotatingdrill stem having a central passage is located within a stationary pipeforming an annular passage surrounding the drill stem. Air is introducedunder pressure through the central passage. It exits from the centralpassage at the location of a bit mounted at the lower end of the drillstern, and carries cuttings and dust upwardly through the annularpassage. A dust diverter is mounted on the stationary pipe just abovethe bit. The diameter of the lower end of the dust diverter is nearly asgreat as that of the bit. The dust diverter, however, narrows toward thelocation at which it is connected to the pipe. The internal diameter ofthe pipe and the external diameter of the drill stern are chosen so thatthe annular passage between them has a cross-section which produces ahigh rising velocity of the air passing through the annular space.Cuttings can thus be carried out efficiently without employing largevolumes of flushing air. The annular space, however, is adequately largeto prevent any accumulation of cuttings within it.

The pressure within the annular passage and within the dust diverter isat a lower pressure than the space outside the dust diverter. Therefore,air carrying dust tends to enter the dust diverter, and does not enterthe atmosphere through the space between the pipe and the wall of thehole being drilled.

Since the air entering the hole passes through the central passage ofthe rotating drill stern, it can be conveniently used to power avertically reciprocating piston arranged to impart a hammering action tothe bit in order to aid cutting.

The apparatus is relatively simple and light in weight. The outer pipeis preferably non-rotating, allowing simple collection of cuttings andconserving rotational power. The most 'important advantage of theapparatus, however, is its ability to produce large diameter holes in asingle pass.

The principle object of the invention, therefore, is to drill largediameter holes in earth and rock quickly and reliably.

Another object is to provide an air drilling system which is not liableto break down as a result of blocking of an air passage.

Still another object is to provide an air drilling system in which airunder pressure serves not only the purpose of removing cuttings, butalso operates a hammering device.

A still further object is to eliminate substantially the escape of dustinto the atrnospherefrom a hole being produced by air drilling.

Still another object of the invention is to provide an air drillingsystem in which drill stem sections can be readily attached to eachother in order to increase the depth of the hole beingdrilled. v

Other objects will become apparent from the following description readin conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS DESCRIPTION OF THE PREFERREDEMBODIMENTS Various mechanisms may be used to effect rotation of thedrill bit. Preferably, however, the entire length of the drill stem isrotated, rotational power being applied at or near the upper end of thedrill stem.

FIG. 1 shows a drill stem section 10 having a bore 12 with asubstantially constant diameter. A bull gear 14 is keyed to section 10,and meshes with a drive gear 16 rotated by a motor 18 (FIG. 5) through ashaft 20.

An air connector assembly 22, having an internal passage 24 bent atright angles, is connected to the upper end of drill stem section 10 sothat passage 24 communicates with passage 12 for the introduction of astream of air downwardly into the drill stem. Packing is provided at 26to prevent leakage at the connection.

The connections between the drill stem sections of the assembly may takevarious forms. Conveniently, tapered threads may be used. At the lowerend of drill stem section 10, tapered threads 28 are provided whichconnect to threads at the upper end 30 of a drill stem section 3 2.

A hollow member 34 has a shoulder 36 at its lower end carrying packing37 which prevents the passage of air upwardly between shoulder 36 anddrill stem section 32 into the interior 38 of member 34. A ring-shapedcap 39 is bolted to the top of member 34 to close interior 38. It allowsstem section 32 to extend through its central opening 40 and downwardlythrough the interior 38 .of member 34.

The outer race 41 of a spherical roller bearing rests on a shoulder 42of member 34. It is clamped in position by cap 39. Stem section 32 isprovided with a shoulder 50 which rests on the inner race 52 of thebearing. A nut 54 is threaded onto stem section 32 and clamps race 52against shoulder 50.

A cylindrical pipe section 56-is welded at 58 to member 34.

A transversely extending tubular member 60 is welded into an opening,the edge of which is indicated at 62. Its internal passage 63 is incommunication with the internal passage 64 of pipe section 56.

Within internal passage 64, stern section 32 is provided with a pair ofshoulders 65 and 66, by which its diameter is increased. lts bore 68,however, remains constant in diameter.

As shown in FIGS. 1 and 3, a ring 70 is welded to the exterior of pipesection 56 at its lower end to provide a flange to which there is bolteda spider 72 having a circular central opening 73 through which stemsection 32 extends. The clearance between opening 73 and the stemsection permits the stern section to rotate freely but supports the stemsection .against substantial radial movement. The spider providesopenings at 74, 76 and 78.

A second and longer pipe section 80 is welded to the underside of spider72.

Tapered threads 84 are provided atthe lower end of stem section 32.These threads couple with threads in member 86. (It should be noted thatthreads 84 and member 86 are duplicated in FIG. 2).

At the lower end of pipe section 80, there is welded a ring 88 fonning aflange to which there is bolted a spider 90. Ring 88 and spider 90 aresimilar to ring 70 and spider 72 respectively.

Pipe section 92 is welded to the underside of ring 90 at 94. Section 92surrounds a drill stem section 96, which comprises an upper section 98in which there is mounted a cylindrical valve member 100 held rigidly inplace within section 98 by a spider 102. Spider 102 is integral with thevalve member. Section 98 has an internal cylindrical wall 104 in whichthe upper end 106 of a piston 108 is arranged to reciprocate vertically.

Lower section 110 of drill stem section 96 is threaded to the uppersection 98. Section 110 is the outer casing of the reciprocating pistondevice. The inner wall 112 of section 110 forms a cylinder in which thelower end 114 of the piston can reciprocate. The diameter of thecylinder formed by wall 112 os larger than the diameter of the cylinderformed by wall 104, and the respective ends 106 and 114 of piston 108differ in diameter accordingly. An internal passage 116 within thepiston leads from an opening 118 in the upper end 106 to a transverseopening 120 in a part 121 of the piston having a reduced diameter belowpart 114. A passage 122 leads from space 124 between wall 112 and thepiston to an opening 126 in projection 128 at the bottom of the piston.A retaining ring 130 is provided in the wall 112 in order to prevent thepiston from moving below the position at which the ring is engaged bythe lowermost shoulder 132 of part 114 when the stem section 134 isremoved.

Drill stem section 134, which acts as an anvil, is keyed by thecooperation of teeth 136 and 138 so that it rotates with drill stemsection 110 while it is allowed to reciprocate vertically under thehammering action imparted by piston 108. The lower limit of itsreciprocation is established by the engagement of shoulder 140 onsection 134 with shoulder 142 at the bottom of stem section 110.

Stem section 134 is rigidly connected to bit 144 through stem section160.

Reciprocating piston drilling devices of the type just described arewell known. Briefly, the operation is as follows: referring particularlyto FIG. 2,- air travelling downwardly through passage 68 passes throughthe central passage 116 in the piston causing-the piston to be liftedsince the effective area underneath the piston is greater than thatabove it. When projection 128 clears the opening in the top of stemsection 134 in which it normally fits, air is allowed to pass intocentral passage 146. The momentum of the piston,however, carries itstill further upwardly so that the flow of air into passage 116 is cutoil by valve 100. The piston then descends violently and imparts a blowto the top of stem section'134. So long as air is supplied, thereciprocation of piston 108 will continue automatically.

It has been assumed that the bit has been resting on the bottom of thehole being drilled. It will be apparent that, if the bit is allowed tohang, the upper end of stem section 134 will be sufficiently spaced fromthe lower end of the pistonthatain will freely flow through the centralpassage of the piston and downwardlythrough passage 146. Under theseconditions, the piston will not reciprocate. 1

A ring 148 is welded at the bottom of pipe section 92, and a spider 150is bolted to the ring. Ring 148and spider 150 are similar to thosepreviously described. A frusto-conical member 152 is welded at itsnarrow end to the underside of spider 150. The diameter at the narrowend is approximately that of pipe section 92.

At the wide end of member 152, there is welded a spider 154 (also shownin FIG. 4). Spider 154 is similar to the spiders previously describedbut larger in size. A ring 156 is bolted to the underside of the spider,and a cylindrical skirt 158 is welded to the ring.

The assembly including member 152, spider 154 and skirt 158 constitutesa dust diverter. The diameter of member 158 should be as large as willbe permitted by the hole being drilled. It should be no larger that thebit diameter, however. If the bit is replaced by one having a largerdiameter, member 158 may be replaced by a member having a largerdiameter. This can be accomplished easily by removing the boltsfastening ring 156 to spider 154 and bolting a substitute skirt and ringassembly in place.

Bit 144 is threaded into an enlarged part 160 of stem section 134. Thebit has a central passage 162 which communicates with passage 146, andwhich has a central opening 164 in a small lead bit 166. Obliquepassages 168 and 170 deliver air from the central passage to cones 172and 174 respectively at the ends of arms 176 and 178. Additional obliqueor transverse passages may be provided as desired.

FIG. 5 shows gear box 180 and a bearing box 182 surrounding drill stemsection 10. Arms 184 and 186 connect the bearing box respectively todrive chains 188 and 190 by which the drilling apparatus may be raisedand lowered.

Air connector assembly 22 is connected to a compressor 192 whichdelivers air to it under a pressure typically 250 lbs. per square inch.Transverse pipe 60 is connected to a chip collection box 194 through aflexible hose 196 which allows for vertical movement of the drillingapparatus. Box 194 has a sloped bottom 196 and a hinged door 198 whichopens under the weight of collected cuttings when a sufficient amounthas been collected. A blower 200 is connected through a flexible hose202 and through an opening 204 to the interior of the box. A baffle 206is positioned within the box so that cuttings entering through opening208 strike it and fall to the bottom. The opening at 204 is on theopposite side of the bafile.

Blower 200 draws a vacuum in the space between the drill stem ends ofthe outer pipe sections. The dimensions of the drill stem and the pipesections are preferably related in such a way that the air velocity inthe space between the drill stem and the pipe. is in the vicinity of3,000 feet per minute. This velocity is sufficient to remove cuttings,but not so great as to produce erosion of mechanical parts. Typically,the outside diameter of drill stem section 32, in the area betweenspiders 72 and 90, would be 5 V4 inches while the internal diameter ofpipe section 80 would be 7 '76; inches.

Substantially lower air velocities may be used t0 accomplish removal ofcuttings if a foam-producing material is introduced into the air streamin accordance with the method described in I US. Pat. No. 3,130,798,issued on Apr. 28, 1964 to Harold J. Schramm and Alfred N. Gustafson.

lnoperation, the air from compressor 192 passes through the drill stem,actuates the'piston which delivers a rapid succession of blows to thebit. The combination of bit rotation and vertical reciprocation producesefi'icient cutting through rock. The air stream not only operates thereciprocating piston, but also emerges through openings at the locationof the bit and carries cuttings upwardly through the annular spacesurrounding the drill stem and to the collection box.

Since blower 200 maintains a negative pressure underneath the dustdiverter, dust produced by cutting tends to enter. the

dust diverter, and does not pass .into the space between the wall of thehole and the pipe sections.

The small diameter of the pipe sections compared to thebit diameterpermits the reduction of high rising air velocities with a minimumvolume of air, and also reduces weight of the drilling equipment.Additional drill stern sections and pipe sections may be added asdrilling progresses. The use of ring and spider assemblies is aconvenient method for attaching pipe sections, and the spiders providelateral support for the rotating drill stem.

In summary, the drilling system in accordance with this in vention makespossible the production of large diameter holes with' minimum air volumeand minimum equipment weight, and provides a relatively dust freecondition for the operator.

1. Apparatus for air drilling large diameter holes comprising arotatable drill stern having a large diameter bit attached to its lowerend,

means for imparting rotational movement to said drill stem, a boreentending through said drill stem and having at least one opening at thelocation of said bit, means for introducing air under pressure into saidbore, a non-rotating pipe surrounding said drill stem, means providing aseal between said pipe and said stem at the upper end of said pipe, anoutlet opening near the upper end of said pipe, means for drawing avacuum at said outlet opening, and means providing an enlarged openingat the lower end of said pipe, said opening having a larger diameterthan said pipe, but no greater than the diameter of said bit. 2.Apparatus for air drilling large diameter holes comprising a drill stemhaving a large diameter bit attached to its lower end,

means for imparting a cutting action to said bit, a bore extendingthrough said drill stem and having at least one opening at the locationof said bit, means for introducing air under pressure into said bore, apipe surrounding said drill stem, means providing an outlet opening nearthe upper end of said pipe, means for drawing a vacuum at said outletopening, and means providing an enlarged opening at the lower end ofsaid pipe, said opening having a larger diameter than said pipe, but nogreater than the diameter of said bit. 3. Apparatus for air drillinglarge diameter holes comprising a drill stem having a large diameter bitattached to its lower end,

means for imparting vertical reciprocatory movement to said bit, a boreextending through said drill stem and having at least one opening at thelocation of said bit, means for introducing air under pressure into saidbore, a non-rotating pipe surrounding said drill stem, means providingan outlet opening near the upper end of said pipe, means for drawing avacuum at said outlet opening, and means providing an enlarged openingat the lower end of said pipe, said opening having a larger diameterthan said pipe, but no greater than the diameter of said bit. 4.Apparatus for air drilling large diameter holes comprising a drill sternhaving a large diameter bit attached to its lower end,

means for imparting rotational movement to said bit, a bore extendingthrough said drill stem and having at least one opening at the locationof said bit, means for introducing air under pressure into said bore,air-powered reciprocating means receiving air from within said bore forimparting a hammering action to said bit, a non-rotating pipesurrounding said drill stem, an outlet opening near the upper end ofsaid pipe, means for drawing a vacuum at said outlet opening, and meansproviding an enlarged opening at the lower end of said pipe, saidopening having a larger diameter than said pipe, but no greater that thediameter of said bit. 5. Apparatus for air drilling large diameter holescomprising a drill stem having a large diameter bit attached to itslower end, means for imparting rotational movement to said bit, a boreextending through said drill stem, at least one opening at the locationof said bit, means for introducing air under pressure into said bore,air-powered reciprocating means receiving air from within said bore forimparting a hammering action to said bit, means for discharging airexhausted from said reciprocating means through said opening, anon-rotating pipe surrounding said drill stern, an outlet opening nearthe upper end of said pipe, means for drawing a vacuum at said outletopening, and

means providing an enlarged opening at the lower end of said pipe, saidopening having a larger diameter than said pipe, but no greater than thediameter of said bit.

6. Apparatus for air drilling large diameter holes comprising arotatable drill stem having a large diameter bit attached to its lowerend,

means for imparting rotational movement to said bit,

a bore extending through said drill stem and having at least one openingat the location of said bit,

means for introducing air under pressure into said bore,

a non-rotating pipe surrounding said drill stem,

means providing a seal between said pipe and said stem at the upper endof said pipe, an outlet opening near the upper end of said pipe, meansfor drawing a vacuum at said outlet opening, and

an opening at the lower end of said pipe for collecting air and cuttingsfrom the bottom of a hole being drilled.

7. Apparatus for air drilling large diameter holes comprising arotatable drill stem having a large diameter bit attached to its lowerend,

means for imparting rotational movement to said drill stem, a boreextending through said drill stem and having at least one opening at thelocation of said bit, means for introducing air under pressure into saidbore,

a non-rotating pipe surrounding said drill stem,

means providing an outlet opening near the upper end of said pipe, meansfor drawing a vacuum at said outlet opening, and

an opening at the lower end of said pipe for collecting air and cuttingsfrom the bottom of a hole being drilled,

said non-rotating pipe comprising a plurality of sections arranged inend-to-end relation, and means for fastening said sections together.

8. Apparatus according to claim 7 in which said drill stem comprises aplurality of drill stem sections arranged in end-toend relationship andmeans for fastening said drill stem section together.

9. Apparatus for air drilling large diameter holes comprising arotatable drill stern having a large diameter bit attached to its lowerend,

means for imparting rotational movement to said drill stem,

a bore extending through said drill stem and having at least one openingat the location of said bit,

means for introducing air under pressure into said bore,

a non-rotating pipe surrounding said drill stem,

means providing an outlet opening near the upper end of said pipe, meansfor drawing a vacuum at said outlet opening, and

an opening at the lower end of said pipe for collecting air and cuttingsfrom the bottom of a hole being drilled, said non-rotating pipecomprising a plurality of sections connected in end-to-end relation, andmeans at each connection for fastening said sections together, each saidfastening means comprising a flange fastened to the end of one of saidsections, a flange fastened to the end of the other section at saidconnection, and means for fastening said flange in face to facerelationship, at least one of said flanges having attached to it spidermeans having a central opening through which said drill stem extends,said spider means providing at least one opening between said drill stemand said pipe for the passage of air and cuttings upwardly to saidoutlet opening near the upper end of said pipe.

10. Apparatus according to claim 9 in which said spider means is anintegral part of the flange to which it is attached.

11. Apparatus according to claim 9 in which said drill stern comprises aplurality of drill stem sections arranged in end-toend relationship andmeans for fastening said drill stem section together.

12. Apparatus for air drilling large diameter holes comprising a drillstem having a large diameter bit attached to its lower end,

means for imparting a cutting action to said bit,

a bore extending through said drill stem and having at least one openingat the location of said bit,

means for introducing air under pressure into said bore,

a pipe surrounding said drill stem,

means providing an outlet opening near the upper end of said pipe, meansfor drawing a vacuum at said outlet opening, 4 means providing anopening at the lower end of said pipe,

and shielding means fastened to the lower end of said pipe forpreventing dust produced by the cutting action of said bit from passingupwardly to the surface through the space between the pipe and the wallof the hole being drilled. 13. Apparatus according to claim 12 includinga skirt having a maximum diameter not exceeding that of said bit andmeans detachably fastening said skirt to the shielding means.

14. Apparatus for air drilling large diameter holes comprising a drillstem having a large diameter bit attached to its lower end.

means for imparting a cutting action to said bit, a bore extendingthrough said drill stem and having at least one opening at the locationof said bit,

means for introducing air under pressure into said bore,

' a pipe surrounding said drill stem,

an opening at the lower end of said pipe for collecting air and cuttingsfrom the bottom of a hole being drilled,

a collection box for cuttings, said box having an inlet opening, anoutlet opening and at least one baffle obstructing a straight pathbetween said inlet and outlet openings,

means providing an opening near the upper end of said pipe,

means for drawing a vacuum,

a conduit connecting said opening near the upper end of said pipe to theinlet opening of said collection box, and means connecting said meansfor drawing a vacuum to the outlet opening of said collection box.

15. Apparatus according to claim 14 in which said conduit is a flexibleconduit.

16. Apparatus according to claim 14 including shielding

1. Apparatus for air drilling large diameter holes comprising arotatable drill stem having a large diameter bit attached to its lowerend, means for imparting rotational movement to said drill stem, a boreentending through said drill stem and having at least one opening at thelocation of said bit, means for introducing air under pressure into saidbore, a non-rotating pipe surrounding said drill stem, means providing aseal between said pipe and said stem at the upper end of said pipe, anoutlet opening near the upper end of said pipe, means for drawing avacuum at said outlet opening, and means providing an enlarged openingat the lower end of said pipe, said opening having a larger diameterthan said pipe, but no greater than the diameter of said bit. 2.Apparatus for air drilling large diameter holes comprising a drill stemhaving a large diameter bit attached to its lower end, means forimparting a cutting action to said bit, a bore extending through saiddrill stem and having at least one opening at the location of said bit,means for introducing air under pressure into said bore, a pipesurrounding said drill stem, means providing an outlet opening near theupper end of said pipe, means for drawing a vacuum at said outletopening, and means providing an enlarged opening at the lower end ofsaid pipe, said opening having a larger diameter than said pipe, but nogreater than the diameter of said bit.
 3. Apparatus for air drillinglarge diameter holes comprising a drill stem having a large diameter bitattached to its lower end, means for imparting vertical reciprocatorymovement to said bit, a bore extending through said drill stem andhaving at least one opening at the location of said bit, means forintroducing air under pressure into said bore, a non-rotating pipesurrounding said drill stem, means providing an outlet opening near theupper end of said pipe, means for drawing a vacuum at said outletopening, and means providing an enlarged opening at the lower end ofsaid pipe, said opening having a larger diameter than said pipe, but nogreater than the diameter of said bit.
 4. Apparatus for air drillinglarge diameter holes comprising a drill stem having a large diameter bitattached to its lower end, means for imparting rotational movement tOsaid bit, a bore extending through said drill stem and having at leastone opening at the location of said bit, means for introducing air underpressure into said bore, air-powered reciprocating means receiving airfrom within said bore for imparting a hammering action to said bit, anon-rotating pipe surrounding said drill stem, an outlet opening nearthe upper end of said pipe, means for drawing a vacuum at said outletopening, and means providing an enlarged opening at the lower end ofsaid pipe, said opening having a larger diameter than said pipe, but nogreater that the diameter of said bit.
 5. Apparatus for air drillinglarge diameter holes comprising a drill stem having a large diameter bitattached to its lower end, means for imparting rotational movement tosaid bit, a bore extending through said drill stem, at least one openingat the location of said bit, means for introducing air under pressureinto said bore, air-powered reciprocating means receiving air fromwithin said bore for imparting a hammering action to said bit, means fordischarging air exhausted from said reciprocating means through saidopening, a non-rotating pipe surrounding said drill stem, an outletopening near the upper end of said pipe, means for drawing a vacuum atsaid outlet opening, and means providing an enlarged opening at thelower end of said pipe, said opening having a larger diameter than saidpipe, but no greater than the diameter of said bit.
 6. Apparatus for airdrilling large diameter holes comprising a rotatable drill stem having alarge diameter bit attached to its lower end, means for impartingrotational movement to said bit, a bore extending through said drillstem and having at least one opening at the location of said bit, meansfor introducing air under pressure into said bore, a non-rotating pipesurrounding said drill stem, means providing a seal between said pipeand said stem at the upper end of said pipe, an outlet opening near theupper end of said pipe, means for drawing a vacuum at said outletopening, and an opening at the lower end of said pipe for collecting airand cuttings from the bottom of a hole being drilled.
 7. Apparatus forair drilling large diameter holes comprising a rotatable drill stemhaving a large diameter bit attached to its lower end, means forimparting rotational movement to said drill stem, a bore extendingthrough said drill stem and having at least one opening at the locationof said bit, means for introducing air under pressure into said bore, anon-rotating pipe surrounding said drill stem, means providing an outletopening near the upper end of said pipe, means for drawing a vacuum atsaid outlet opening, and an opening at the lower end of said pipe forcollecting air and cuttings from the bottom of a hole being drilled,said non-rotating pipe comprising a plurality of sections arranged inend-to-end relation, and means for fastening said sections together. 8.Apparatus according to claim 7 in which said drill stem comprises aplurality of drill stem sections arranged in end-to-end relationship andmeans for fastening said drill stem section together.
 9. Apparatus forair drilling large diameter holes comprising a rotatable drill stemhaving a large diameter bit attached to its lower end, means forimparting rotational movement to said drill stem, a bore extendingthrough said drill stem and having at least one opening at the locationof said bit, means for introducing air under pressure into said bore, anon-rotating pipe surrounding said drill stem, means providing an outletopening near the upper end of said pipe, means for drawing a vacuum atsaid outlet opening, and an opening at the lower end of said pipe forcollecting air and cuttings from the bottom of a hole being drilled,said non-rotating pipe comprising a plurality of sections connecTed inend-to-end relation, and means at each connection for fastening saidsections together, each said fastening means comprising a flangefastened to the end of one of said sections, a flange fastened to theend of the other section at said connection, and means for fasteningsaid flange in face to face relationship, at least one of said flangeshaving attached to it spider means having a central opening throughwhich said drill stem extends, said spider means providing at least oneopening between said drill stem and said pipe for the passage of air andcuttings upwardly to said outlet opening near the upper end of saidpipe.
 10. Apparatus according to claim 9 in which said spider means isan integral part of the flange to which it is attached.
 11. Apparatusaccording to claim 9 in which said drill stem comprises a plurality ofdrill stem sections arranged in end-to-end relationship and means forfastening said drill stem section together.
 12. Apparatus for airdrilling large diameter holes comprising a drill stem having a largediameter bit attached to its lower end, means for imparting a cuttingaction to said bit, a bore extending through said drill stem and havingat least one opening at the location of said bit, means for introducingair under pressure into said bore, a pipe surrounding said drill stem,means providing an outlet opening near the upper end of said pipe, meansfor drawing a vacuum at said outlet opening, means providing an openingat the lower end of said pipe, and shielding means fastened to the lowerend of said pipe for preventing dust produced by the cutting action ofsaid bit from passing upwardly to the surface through the space betweenthe pipe and the wall of the hole being drilled.
 13. Apparatus accordingto claim 12 including a skirt having a maximum diameter not exceedingthat of said bit and means detachably fastening said skirt to theshielding means.
 14. Apparatus for air drilling large diameter holescomprising a drill stem having a large diameter bit attached to itslower end. means for imparting a cutting action to said bit, a boreextending through said drill stem and having at least one opening at thelocation of said bit, means for introducing air under pressure into saidbore, a pipe surrounding said drill stem, an opening at the lower end ofsaid pipe for collecting air and cuttings from the bottom of a holebeing drilled, a collection box for cuttings, said box having an inletopening, an outlet opening and at least one baffle obstructing astraight path between said inlet and outlet openings, means providing anopening near the upper end of said pipe, means for drawing a vacuum, aconduit connecting said opening near the upper end of said pipe to theinlet opening of said collection box, and means connecting said meansfor drawing a vacuum to the outlet opening of said collection box. 15.Apparatus according to claim 14 in which said conduit is a flexibleconduit.
 16. Apparatus according to claim 14 including shielding meansfastened to the lower end of said pipe for preventing dust produced bythe cutting action of said bit from passing upwardly to the surfacethrough the space between the pipe and the wall of the hole beingdrilled.